1. Field of the Invention
This invention relates to a film transfer method. More particularly, it relates to a method of transferring a film having functional features such as producing a piezoelectric effect and adapted to be suitably used for an actuator, a sensor, a liquid droplets ejector or some other applications.
2. Related Background Art
Currently, massive research efforts are being paid for developing devices using functional films. It is expected to realize marvelous functional features by forming thin films of such functional materials and applying them to various devices.
For example, various researches are being made on devices such as piezoelectric elements, sensors and non-volatile memories that can be realized by utilizing various physical properties of ferromagnetic substances including a piezoelectric effect, a pyroelectric effect and a polarization inversion effect. Particularly, ink-jet systems adapted to eject ink by using piezoelectric elements have been developed rapidly for various applications including printers, copying machines and facsimile machines in recent years because they can record high definition and high quality images including color images at high speed and high density if they come out with small dimensions. It should be noted, however, that there is a strong demand for technologies that can realize higher quality and higher definition images and piezoelectric elements comprising a film that shows a piezoelectric effect are currently regarded to be highly promising for the next generation high quality and high definition recording technologies.
While various method may be used for forming a film showing a piezoelectric effect, Japanese Patent Application Laid-open No. 6-290983 describes a method of forming PZT (Pb(Zrx,Ti1-x)O3; lead zirconate titanate) with improved crystallinity by using RF sputtering. Japanese Patent Application Laid-open No. 11-220185 describes a method of forming PZT oriented to the (100) plane by using the sol-gel method and controlling the temperature for decomposing the precursor substance.
Many oxides can be used for making functional thin films. Particularly, since a film showing a piezoelectric effect is normally made of a compound oxide, temperature higher than 600xc2x0 C. will be required for crystallizing such a substance. For crystallization, a film may be formed in a non-heating film forming process at temperature between room temperature and about 200xc2x0 C. and subsequently annealed at temperature higher than 600xc2x0 C. Alternatively, a crystallized film may be formed by heating a substrate to temperature above 600xc2x0 C. for the purpose of simultaneous crystallization. In any case, a single-crystal substrate that can withstand high temperature needs to be used for forming a film showing a piezoelectric effect because temperature higher than 600xc2x0 C. is involved in the crystallization process. While the single-crystal substrate may be made of MgO or SrTiO3, such a substrate is normally very costly and hence it is disadvantageous from the viewpoint of cost if it is consumed in a single film forming process.
Additionally, after forming a film showing a piezoelectric effect on a single-crystal substrate, the substrate is bonded to another substrate and dissolved typically by means of hot phosphoric acid. For instance, Japanese Patent Application Laid-open No. 10-286953 describes a method of removing a MgO substrate by means of phosphoric acid after forming PZT on the substrate and bonding the substrate to a vibrating plate. However, such a process is very disadvantageous from the viewpoint of cost and throughput and hence not feasible for mass production.
These problems and other problems can advantageously be avoided when the film formed on a substrate is transferred onto some other substrates because the first substrate is not damaged.
The present invention makes it possible to transfer a film onto a substrate that is not adapted to directly form a film thereon without damaging the costly single-crystal substrate on which the film is originally formed by using an easy means having a simple configuration and utilizing a lift-off layer.
According to the invention, there is provided a film transfer method for transferring a film from a first substrate onto a second substrate, said method comprising steps of:
forming a lift-off layer on said first substrate;
forming a film to be transferred on said lift-off layer;
bonding said film to be transferred onto said second substrate; and
etching said lift-off layer by means of an etchant and separating said second substrate from said first substrate.